1. Field of the Invention
The present invention relates to a chip antenna in which an antenna element having a line antenna portion is buried in a resin molding, and a method of manufacturing the chip antenna.
2. Description of the Prior Art
One of chip antennae has a structure in which a metal antenna element having, for example, a meander line pattern shape formed thereon is buried in a resin molding. This type of chip antenna is manufactured by setting an antenna element in a mold for injection molding and then injection-molding a dielectric resin in the mold.
At this time, a gate mark originated from the injection molding of the dielectric resin in the mold for injection molding remains on the end face of the resin molding. A gate mark is undulations of about several hundred micrometers, and is negligible for ordinary resin moldings. In case of a chip antenna, however, a gate mark increases or reduces the amount of a dielectric near the antenna element and thus influences the antenna characteristics, such as the resonance frequency.
Terminal portions which are provided continuously to the antenna element protrude from the resin molding. In addition, the antenna element is simply physically contacted to the resin molding. Applying stress on the resin molding from the terminal portions is therefore likely to deform the resin molding. The deformation of the resin molding may separate the resin molding from the antenna element or cause cracks in the resin molding.
At the time the dielectric resin is injection-molded in the mold for injection molding in which the antenna element is set, the strong flow of the dielectric resin near the dielectric inlet port (gate portion) deforms, for example, a meander line pattern shape (line antenna portion), thereby changing the antenna characteristics.
Accordingly, it is an object of the present invention to provide a chip antenna whose antenna characteristics are not influenced by the state of a gate mark remaining on a resin molding, and a method of manufacturing the chip antenna.
It is another object of the present invention to provide a chip antenna which does not suffer separation of a resin molding and cracking thereon, and a method of manufacturing the chip antenna.
To achieve the objects, a chip antenna according to the present invention is characterized in that of margins of the resin molding around an antenna element buried in a resin molding, a margin on that side of the resin molding where an injection molding originated gate mark remains is larger than margins on other sides where there is no gate mark.
A xe2x80x9cmarginxe2x80x9d of the resin molding mentioned here is an area which does not substantially overlap the antenna element at the peripheral portion of the resin molding as seen planarly. This design can set the distance from the antenna element to the gate mark longer, so that the influence of the projections or indents of the gate mark on the antenna characteristics can be decreased. It is also possible to reduce the stress applied to the interface between the antenna element and the resin molding.
Another chip antenna according to the present invention has a structure where an antenna element is buried in a resin molding having a predetermined chip shape and terminal portions provided continuously to the antenna element protrude from the resin molding. Particularly, the chip antenna is characterized in that those portions of the resin molding with the predetermined chip shape where the terminal portions are led out are dented from levels of portions around those portions.
As this structure can make larger a resin molding area (margins) around those portions of the resin molding from which the terminal portions protrude, it is possible to increase the mechanical strength for receiving the stress applied to the resin molding from the terminal portions. This can prevent separation of the resin molding and cracks from being formed thereon.
A method of manufacturing a chip antenna according to the present invention sandwiches those portions of terminal portions provided continuously to an antenna element which are led out from a resin molding between an upper die and a lower die of a mold for injection molding, positions the antenna element in a cavity of the mold and then injects a dielectric into the cavity to bury the line antenna portion with the dielectric. Particularly, the method is characterized in that those portions of the mold for injection molding which sandwich the terminal portions from above and below are the dies that are so shaped as to protrude toward the cavity.
When an antenna element has a capacitance-adding portion at a distal end of a line antenna portion, a dielectric is injected into the cavity from outward of the capacitance-adding portion as seen from a center of the antenna element. Further, when the line antenna portion of the antenna element has meander line pattern shapes with different line widths and pitches formed at both ends, the dielectric is injected into the cavity from, for example, that side of the meander line with the wide line width.
Determining the position of the injection of a dielectric into the cavity this way can prevent the antenna element from being deformed by the strong flow of the dielectric resin near the dielectric inlet port (gate portion).